One important performance parameter for power supplies, for both linear and switching power supplies, is their load transient response. Load transient response measurements show the ability for a power supply to respond to abrupt changes in the current demand from a load (e.g., a microprocessor) referred to as the load current. The load transient is a load current step, which injects a disturbance into the output of the power supply.
Testing a power supply at different output voltages for a particular load current step can be a time consuming process. Using an off-the-shelf electronic load allows for easy configuration of the load step, but it is ineffective for providing relatively fast load transient responses (e.g., greater than 1 A/μs) due to the inductance of the cables connecting the power supply to the electronic load. Physically bolting the power supply to the electronic load may help to reach the maximum slew rate of the electronic load, but is impractical for most transient load testing.
Another known solution for a load transient circuit is a field effect transistor (FET) connected in series with a resistor (R). An advantage of this arrangement is that the FET and R can be placed next to a device under test (DUT) output for significantly faster slew rates. Disadvantages of this arrangement include the peak load current (Ipeak) will vary based on the DUT's output voltage (Vout) for a given R value, and to obtain a different fixed Ipeak across Vout, the R value needs to be changed. As a result, this arrangement slows down validation test execution of a DUT.
As the power density of switching power supplies increases and their footprint decreases, the switching frequencies used also generally increases. Validating the operation of a variety of a newly designed electronic device (e.g., a silicon-based switching power supply) for potential end customer applications can benefit from faster transient response testing, both in the slew rate and the pulse repetition frequency.